Military aircraft utilize racks located beneath the wings, the fuselage, and/or in the main weapons bay to carry and dispense stores upon command. Stores may be used to contain munitions, i.e. bombs, or to contain other material to be dropped from the aircraft, i.e. rockets or missiles, upon command from the cockpit, for example. Conventionally, an ejector rack includes a release mechanism which is activated to mechanically release and, subsequently, forcibly eject the stores from the aircraft. Most ejector racks, at one time, utilized pyrotechnic (explosive) cartridges which, upon ignition, generate high pressure gas for actuating the mechanical release mechanism, as well as providing high pressure gas to forcibly eject the stores from the racks mounted on the aircraft.
A characteristic of an ejector rack powered by a pyrotechnic (explosive) cartridge is a short, very high pressure pulse. This high pressure pulse allowed for the removal of the sear from the pedestal of the retaining hook and release of the store. The cartridges were somewhat unreliable, however, and their handling, maintenance, and costs were significant.
In order to avoid problems associated with the pyrotechnic cartridges, the ejector racks migrated to cold gas (pneumatic) systems. As such, an ejection system includes an on-board source of pressurized gas, a suspension mechanism for mounting the store on the aircraft, and an actuation system for driving the release mechanism between closed and open positions. By using compressed air to activate the ejector pistons and push the store through the air stream, pneumatic ejection racks have many advantages over traditional ejection racks which use pyrotechnic cartridges. The pneumatic ejection racks take advantage of the elimination of pyrotechnic cartridges and hazardous waste disposal, reduce the need for maintenance and spare parts, and have a longer life span thereby enhancing life cycle cost and overall system affordability.
The application of the pneumatic technology to the airborne store suspension and release systems is known in the prior art. One of the earliest examples is in U.S. Pat. No. 4,204,456 to Ward in 1980, titled Pneumatic Ejector for Bomb, which discloses a pneumatically operated piston with a radial clearance to the gas tight cylinder to allow for charging of the air or other gas into both sides of the piston. Ejection is then achieved by using a solenoid controlled valve to release gas pressure from the lower side of the piston at a faster rate than the leakage past the piston. More recent art on pneumatic racks is presented by Jakubowski et al., in U.S. Pat. No. 7,147,188 in 2006, titled Aircraft Store Ejector Rack Systems And Methods, which discloses a sequential operation of opening store retention hooks and releasing pressurized gas to eject the store by means of a staged actuator assembly.
Such pneumatic actuation systems include an accumulator for receiving and storing pressurized gas from a source, which may or may not be located on board the aircraft. Actuation of a control valve causes a primary valve to move from a closed position to an open position. This action vents the pressurized gas from a lower side of a hook release piston to move the hook release piston downward to unlock the store retention hooks. Subsequent opening of the primary valve releases the pressurized gas to ejector cylinder to eject the store. The pressure inside the ejector cylinders prevents automatic resetting of the ejector pistons to the original positions and must be vented after store release to allow the ejector pistons to retract to the original positions for the next store to be loaded.
The pneumatic ejection system includes an accumulator, or a pneumatic power module (PPM). The PPM represents one of the largest and highest cost components in an ejector rack assembly. The PPM is a single unit which combines a pressure storage reservoir with a valve assembly or valve manifold. The first stage of the valve assembly disengages the sear from the pedestal of the retaining hook, thereby allowing release of the store. The second stage of the valve assembly opens the path for the pressurized gas to the ejector pistons, thereby ejecting the store away. The complication is in avoiding flow restrictions to enable faster and more consistent valve response times and higher store ejection velocity, in an energy-efficient manner.
As will be explained, the present invention provides an efficient valve manifold design, utilizing few parts, for a pneumatic ejection system. The valve manifold design of the present invention minimizes flow path restrictions and provides a fast acting valve actuation response with minimum variability to unlock the hooks and eject the store. The present invention also allows the de-energized eject valve to quickly return to the closed position by the combined forces of the spring and the pressure in its main chamber. The quick closure of the eject valve optimizes the residual pressure in the vessel and prevents gas flow downstream of the eject valve. The eject valve at the closed position also vents the hook release valve and ejector cylinders so that the ejector pistons can automatically reset to the original positions after store release. The ejector pistons and ejector cylinders are then ready for the next store to be loaded.